You ignore the woman as she stares and smiles.
Your testicles, more sensitive than ever, seem to be smoothing out. They look so strange and you touch them in the hopes of discovering some key to stopping the change, but touching them seems to light a fire like you have never experienced. You are frozen as the sensation cripples you. Your testicles slowly retreat into your body and you watch, helpless to stop them. Your scrotum smooths out and flattens against the bottom of your body trunk. You stare in horror. They are gone, and you can't get them back. A word fills your mind and causes you to shiver: ovaries. Your male parts have become female.
And with that thought, you turn your attention to your penis. Just minutes before it was erect and thrusting in the best sex you had ever had. Now it is no longer itself. Not that it is flaccid, rather, its length retracts and its girth expands. The whole penis is becoming just the head, and the opening stretching up and down. After a minute, it no longer looks like a penis at all, but more like its opposite. Another minute later, and your penis opening has grown labia and your head has reshaped itself as a plump vaginal protrusion. You expect it to further retreat, but it does not. You've never seen a vagina so fat, and you reach down to pull it up and let go. It bounces back firmly, there to stay.
You think back to the sex you just had, and your shoulders slump as you realize you will never penetrate a woman ever again. The thought occurs to you that if you were to have sex again, it would be you who is penetrated. You suddenly feel very vulnerable.
Your shake your head as the changes stop. You hear the woman laughing. You look up into her eyes and see in them a horrible greed, a hunger that belies her otherwise beautiful features. "Well don't stop now," she coaxes. "Let's see what female animal you've become."